Inversion domains and the mechanical properties of Gamma-2 (Cu-Al) intermetallic compound

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u s i n g a d i a m o n d saw. T h e s e s p e c i m e n s h a v e t h e f o r m of p a r a l l e l o g r a m s w i t h a b a s e o f 2 × 2 m m a n d a h e i g h t of 5 m m . T o c h e c k t h e v a r i a t i o n s of the m e c h a n i c a l p r o p e r t i e s w i t h t h e w i d t h of t h e i n v e r s i o n d o m a i n s , a n u m b e r of s p e c i m e n s o f t h e s e t h r e e c o m p o s i t i o n s w e r e h e a t e d t o 8 5 0 ° C f o r 15 m i n a n d t h e n c o o l e d r a p i d l y ( 3 0 ° C / m i n ) i n a n e f f o r t t o r e t a i n a fine r i b b o n s t r u c t u r e . A n o t h e r s e t o f s p e c i m e n s w e r e c o o l e d s l o w l y (2 × 1 0 - 2 ° C / m i n ) f r o m the a n n e a l i n g t e m p e r a t u r e i n a n a t t e m p t t o d e v e l o p t h e wide r i b b o n s t r u c t u r e . T h e r e s u l t a n t d o m a i n ' s w i d t h in t h e s p e c i m e n s w i t h c o m p o s i t i o n 34.5 a t . p c t A I w a s a r o u n d 0.1 ~tm f o r t h e r a p i d c o o l e d m a t e r i a l a n d 1 ~tm f o r t h e s l o w l y c o o l e d . N o d o m a i n s t r u c t u r e was o b s e r v e d in t h e s p e c i m e n s o f 3 1 . 5 7 a n d 35.4 a t . p c t A I . A t t h e s e c o m p o s i t i o n s t h e a l l o y s h o w s

F i g . 1--Inversion d o m a i n s in Cu-34.5 a t . pet A 1 . T h e m i c r o g r a p h s h o w s a r e g i o n of r i b b o n d o m a i n and t r i a n g u l a r d o m a i n s s t r u c t u r e . 143 n - b e a m d a r k - f i e l d i m a g e s .

F i g . 2--Coarsening of the r i b b o n d o m a i n s d u r i n g a very s l o w cooling from 550°C i n Cu-34.5 a t . pct A1.

ISSN 0360-2133 / 79/ 0312-0385500.75/0 © 1979 AMERICAN SOCIETY FOR METALS AND T H E METALLURGICAL SOCIETY OF AIME

VOLUME 10A, MARCH 1979-385

a few isolated dislocations always associated with a f r i n g e pattern. This f r i n g e pattern has properties s i m i l a r t o those produced by inversion domains (Fig.

160

O

samples quenched air f r o m 8 5 0 ° C

in

3) .6 The high pressure experiments were c a r r i e d out up t o 12 Kb in an apparatus constructed in Case Western R e s e r v e University and which has been described in detail previously2 The compressive stress-strain curves are shown in Fig. 4, the specimens with composition 31.57 and 35.4 a t . pct A1 showing s i m i l a r behavior with respect to the applied hydrostatic pressure. Plastic flow in both mat e r i a l s can be induced at 2 Kb and the amounts of plastic s t r a i n and the plastic fracture strengths are inc r e a s e d similarly with further i n c r e a s e in the p r e s s u r e . However the work-hardening r a t e s differ for t h e s e samples. The specimens with inversion domains (34.5 a t . pct A1) show quite different yield behaviors for the two



E ~140

samples slowly cooled

~0 uJ

ku~ 1 2 0 r~ .J uJ >,~, 100

--

I 30

I 32

I ~ I 34 36

I

I at ° l ° A I

F i g . 5--Influence of the c o m p o s i t i o n o n the y i e l d behavior of the g a m m a - 2 phase. A p e r i o d i c a r r a y of inversion d o